Your assignment: Design a post-apocalyptic communication system

I'm a programmer but weak on hardware so I'd appreciate your help. In a novel I'm writing there are about one hundred underground cities housing one million people in the US; the rest of our population is dead. Somewhat smaller percentage of survivors in Europe and Asia. We have several years warning and want to establish a communication system - internet and television - for the survivors, including - if possible - communication with Europe and Asia via undersea cables. The cities have plenty of energy available but there will be none between cities, so I wonder if the distances between nodes will make it impractical.